In a semiconductor module mounted to a power electronics device or an in-vehicle electronic apparatus, an internal component might be fractured during an operation due to a thermal load or a dynamic load. In the loads that cause the failure, there is a load that causes a failure when it is applied once to the device. There is also a load that causes a damage, and the caused damage is accumulated to cause the fracture of the device, when this load is applied many times. For example, a temperature variation generated due to the change in the operation state of the device causes repeated stress to a electrical joint (e.g., a electrical joint between a device and an electrode, or a solder electrical joint) by a difference in a linear expansion coefficient between components such as a device or a circuit board. When the device is installed in a condition in which a dynamic stress is applied thereto, the repeated stress is generated due to an application of inertia force. There may also be a case where the variation in the dynamic stress is superimposed on the repeated thermal load to cause repeated composite load.
Stress or distortion applied once to the device does not cause a fracture, but the repeated stress or distortion caused by the repeated load might cause a fracture.
On the other hand, there is a technique of a health monitoring as a technique of making a diagnosis of a product, which is to be used for a long term, and predicting a life to failure, in order to exchange service parts at an appropriate timing. The health monitoring technique includes various methods. One of examples for the above-mentioned electronic apparatus is to predict a life to repeated load.
Electronic apparatuss in recent years can be provided with sensors such as a temperature sensor or an acceleration sensor. Various measures can be taken according to a condition by monitoring the state of the operated device.
For example, a temperature of a computation processing component such as a central processing unit (CPU) is always sensed, and when the temperature rises to exceed a threshold value, a computation load is forcibly reduced to prevent a failure due to the temperature rise. Alternatively, an acceleration and tilt of the device are sensed by the acceleration sensor, whereby an operation of retracting a head of a hard disk drive, or an operation of starting an application designated by a user can be carried out.
These sensors are expected to be used to predict a fatigue life to the above-mentioned repeated load.
However, in such known techniques, a life cannot appropriately be predicted when a composite load formed by the superimposition of the thermal load and the dynamic load is applied. In a power semiconductor module, a semiconductor device and an insulating circuit board, as well as a circuit board and a heat spreader, are bonded through a thin-film metal bonding layer in order to secure a heat dissipation path to a cooling structure. In power semiconductor modules, semiconductor devices or the semiconductor circuit board and the circuit board are connected with a conductive member such as a metal wire or a metal thin film. In this case, a large amount of heat is locally caused on the connection surface of the semiconductor device and the conductive member. Therefore, the electrical joint immediately under the connection surface might be fractured, and there is a fear of deterioration in the heat dissipation performance due to the fracture on the electrical joint. For example, in the power semiconductor module bonded with a thin-film metal bonding layer, a fracture is not limited to be caused from a corner of the module. Even if the fracture is caused from the corner, a fracture life of the corner is far apart from the fracture life of the target electrical joint. Therefore, this is not appropriate for detecting a sign of a failure. In the known techniques, it might be difficult to preliminarily detect the sign of the failure.